Say for example you have a product page, and you wish to have 3 images of the product. You can create a field call images, and have a list of all the sources of the images, e.g. image1.jpg, image2.jpg, image3.jpg. Then you can create an array for your images and run a loop to display them.
Alternatively you can create a new table called images, that can match the product up with the images, e.g.
Product ID Image
Which way is the best? and why?